The present invention relates generally to improvements in a longitudinally position adjusting or shifting device including a stationary member having a guide groove and at least one driven member having a guide pin engaging the guide groove, wherein in the event of an unwanted external force being exerted on the driven member, a smooth operation of the shifting device is ensured, and it relates more particularly to a shifting device for axially adjusting the positions of lenses mounted in a lens barrel.
Generally, whether a lens barrel is mounted on a camera body or remains separate from the camera body, such occasions often arise that the lens barrel undergoes mechanical shock due to its being dropped from a users hand or due to an inadvertent impingement on a hard object.
A shifting device for axially adjusting lenses mounted in a lens barrel, in general includes a guide pin and a guide cam groove receiving the guide pin, and the shifting or adjusting operation effected by the shifting device is accomplished by sliding the guide pin along the cam groove under the guidance of the latter.
Should any shock be exerted on such a lens barrel, the impingement of the guide pin on the control face of the cam groove results in a breakage or rupture of or damage to an element of the shifting device thereby disabling the device from accomplishing a subsequent shifting operation a smooth and accurate manner.
A known device, as shown in FIG. 1 by way of example, is a lens barrel for two-group type zoom lens includes a shifting device for a first movable lens which is alone described for the simplicity of explanation. Linear groove 3 and 11 extending in the direction of the optical axis of the lens, are formed at the internal face of a stationary sleeve 2 which is integrally formed with a barrel mount 1 for attaching the lens barrel to a camera body. A cam sleeve 8 is fitted in the stationary sleeve 2, and is slidingly rotatable position therein at a fixed longitudinal position on the axis. Cam sleeve 8 is provided with peripheral cam grooves 5 and 12. A connecting pin 20 carried by cam sleeve 8 extends radially outwards through an annular groove in stationary sleeve 2, and engages a recess 7 provided in the inside peripheral face of a zoom ring 6, whicn, in turn, engages the outer face of stationary sleeve 2 and is rotatable at a fixed position on the axis of the stationary sleeve.
A first movable lens frame 14 and a second movable lens frame 17 are slidably fitted in cam sleeve 8, and guide pins 4 and 9 respectively carried by frames 17 and 14 extend radially outwards through cam grooves 5 and 12 respectively in slidable engagement therewith, and also slidably engage in linear grooves 3 and 11.
Engaged with a screw thread or a helicoid provided on the inner wall of first movable lens frame 14 is a screw thread or helicoid 15 provided on the outer peripheral surface of a lens holding frame 16 carrying a first movable lens 19. Lens holding frame 16 is formed with a lens barrel front portion 13 and a focusing ring 10 loosely fitted on stationary sleeve 2 and integral with lens barrel front portion 13.
In operation of the adjusting mechanism, if focusing ring 10 is rotated, lens holding frame 16 carrying first movable lens 19 is shifted frontwards or rearwards by means of helicoid 15, thereby focusing the lens system. If zoom ring 6 is rotated, then cam sleeve 8 is rotated by means of the pin 20, together with zoom ring 6, whereby follower or guide pins 4 and 9 are guided by cam grooves 5 and 12 as well as linear grooves 3 and 11, respectively, thereby shifting second movable lens frame 17 and first movable lens frame 14 in the axial direction at a predetermined ratio or rate relationship, respectively, whereby zooming is achieved.
In the event of a shock being applied to or exerted on lens-barrel front portion 13, such shock causes, for example, guide pin 9 and cam groove 12 to collide with each other, with a resultant breakage or rupture of or damage to one or both of these elements which disables the smooth and accurate operation of the zooming mechanism in the subsequent photography, and impairs the proper movement of the first movable lens frame 14. In the worst case, breakage of cam groove 12 results, disabling the rotation of the cam sleeve 8 and hence rotation of the zooming ring 6. In order to avoid the above-described drawbacks, an arrangement may be employed in which a protective lens barrel covering the outer periphery of the holding frame 16 for first movable lens 19 is mounted on the lens barrel against movement in the direction of the optical axis, and the front portion of the protective lens barrel assumes a position to project a considerable distance forward of the front portion of holding frame 16, when the latter is set to the front extremity by the focusing operation and the zooming operation, so that holding frame 16 will not project externally of the protective lens barrel.
Such an arrangement however, is accompanied by a resulting high complexity in the construction of the lens barrel, as well as in difficulty in design of the rotating focusing ring 10. Furthermore, in order to prevent light rays incident on the first movable lens 19 assuming a most retracted position, from being interrupted by the front portion of the protective lens barrel, the diameter of the protective lens barrel must be increased, resulting in an increased size of the overall lens barrel, and hence an awkward and bulky lens barrel.